Field of the Invention
This invention relates to an improved process for the production of high-quality, fine-particle, solid pourable or free-flowing useful materials or mixtures of useful materials suitable for use as and/or in wetting agents, detergents and/or cleaning products, from aqueous preparations thereof. The process according to the invention involves one or more drying steps using superheated steam as the drying gas.
The spray drying of aqueous preparations of useful materials of the type mentioned, which are widely used, for example, as laundry detergents, has been carried out on an industrial scale for decades. Hot air or mixtures of air and hot waste combustion gases are used as the drying gas stream. Washing powders or useful materials and/or mixtures of useful materials for the production of laundry detergents in pourable and free-flowing powder form are produced in corresponding spray drying towers, generally at ambient pressure, either in co-current or more often in countercurrent.
In their earlier application DE-A 40 30 688, applicants describe a process for the production of solid, fine-particle pourable and free-flowing useful materials or mixtures thereof for wetting agents, detergents and/or cleaning products from aqueous preparations thereof, superheated steam being used as the drying hot gas stream and drying of the particulate material being terminated before it is endangered by heat. If necessary, the long-term pourability and free-flow of the material thus partly dried is ensured by addition of mixture constituents which are capable of binding limited quantities of water. In addition to or instead of this measure, the particulate material may also be aftertreated to homogenize its residual moisture content and/or after-dried under conditions which do not affect the useful material. The teaching of the invention described hereinafter is concerned with a specific embodiment of this process according to the earlier application cited above. The teaching according to the invention seeks to enable high-quality useful materials or mixtures of useful materials of the type in question to be obtained where superheated steam is used as the drying gas. The problem addressed by the present invention will become clear from the following considerations presented purely by way of example:
The requirements which high-quality detergents, particularly laundry detergents, are now having to satisfy in practice are not confined to performance expectations. The visual appearance, for example a light color in the case of laundry detergents, and other physical properties, such as free flow, a high apparent density, rapid dissolution in water and good dispensing properties and the like, are also important requirements.
The problem addressed by the present invention was to provide optimized conditions for the application in question of drying useful materials with superheated steam as drying medium to enable the high-quality useful materials or mixtures of useful materials to be obtained in the dry state.
It is important in this connection to bear in mind the fact that practical experience in the application of drying processes using superheated steam as the drying gas has been very limited up till now although, basically, this technology has been known since the beginning of this century and has been repeatedly described in the literature. Earlier application DE-A 40 30 688 deals in detail with the relevant prior-art literature. Reference is made here to the corresponding observations in the earlier application and solely to the following publications which in turn cite numerous publications on this subject: A. M. Trommelen et al. "Evaporation and Drying of Drops in Super-heated Vapors" AIChE Journal 16 (1970) 857-867; Colin Beeby et al. "STEAM DRYING" Plenary Lecture, Proc. 4th Int. Drying Sym. Kyoto (eds. R. Toei and Arun S. Mujumdar) 1984, Vol. 1, 51-68 and W. A. Stein "Berechnung der Verdampfung von Flussigkeit aus feuchten Produkten im Spruhturm (Calculating the Evaporation of Liquid from Moist Products in Spray Drying Towers)" Verfahrenstechnik 7 (1973), 262-267.